1. Field of the Invention
This invention concerns starter drives and more specifically starter drives of the types used in cranking small internal combustion engines.
2. Description of the Prior Art
In providing an electric start capability for small internal combustion engines such as are used in powering garden tractors, etc., the starter pinion gear used to rotate the engine flywheel is often unenclosed by the flywheel housing, contrary to designs for car and truck starters. Also, the environment in which such equipment is operated is typically one in which foreign matter could become lodged in the various exposed components thereof such as the starter assembly. Such starters commonly utilize a design wherein a pinion gear is moved axially into engagement with the flywheel gear teeth by an inertia drive arrangement including a threaded engagement between a screw thread by the starter shaft and the pinion gear tending to cause axial movement of the pinion gear upon rotation of the starter shaft due to inertia of the pinion gear. The pinion gear moves axially against a fixed stop which locates the pinion gear axially so as to properly engage the flywheel gear teeth.
These designs thus can become wholly or partially inoperative if dirt or other foreign matter becomes lodged in the space between the pinion gear and the fixed stop, since the axial movement of the pinion gear would thereby be interfered with.
This problem has heretofore been recognized and attempts to solve this problem have included shielding means adapted to enclose this space to prevent the entrance of dirt, grime or other such contaminants.
Examples of these arrangements are found in U.S. Pat. Nos. 3,690,188; 3,124,694; and 2,987,059. A related arrangement is also shown in U.K. Pat. No. 804,626, published Nov. 19, 1958. However, all of these patents have the common feature that they are supported either partially or wholly on the pinion gear so as to tend to be rotated therewith during the axial movement described, and as such tend to be loosened by the sudden stopping and starting of rotation and axial movement of the pinion gear. This factor is aggravated by the constraints the mounting on the pinion gear (or an extension thereof) imposes, i.e., the shield is either simply overhung unsupported at its free end or slidably mounted on the fixed stop, such that it is not positively retained.
It is accordingly an object of the present invention to provide a shield arrangement for starter motors of the type described in which a positive retention of the shield is provided, and which the loosening effects of movement of the pinion gear during starting cycles is avoided.